Double dewaxing process



United States Patent 3,318,800 DGUBLE DEWAXING PROCESS William H. Ringler, Cleveland, Ohio, assignor to The Stagzlard Oil Company, Cleveland, Ohio, a corporation of into Filed Sept. 30, 1963, Ser. No. 312,672 Claims. (Cl. 20833) This invention relates to the manufacture of low pour point oils and more particularly pertains to the manufacture of low pour point oils and useful waxes from waxy crude oils by a novel double dewaxing process.

It has been suggested to dewax waxy crudes by a single dewaxing step to give relatively low pour point oils but such a process is usually not practical because the recovered wax is not saleable nor can it be readily purified and separated into a saleable condition.

The dewaxing process currently used is known as the solvent dewaxing process wherein a solvent mixture of (1) a ketone solvent and (2) an aromatic solvent is used to precipitate wax from waxy crude oils usually at below ambient temperature. The current process contemplates the dewaxing of wax bearing distillate lube oil fractions with liquid mixtures composed of a wax anti-solvent liquid and an oil solvent liquid. Current practice provides for the wax anti-solvent to be an aliphatic ketone such as acetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl isopropyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone or other allphatic ketones containing up to about 8 carbon atoms and mixtures of these ketones. The wax solvent liquid is usually an aromatic solvent such as benzene, toluene, xylenes, cumene and the like. For instance, US. Patent No. 1,802,942 discloses the dewaxing of wax containing distillates with a mixture of acetone and benzene; and US. Patent No. 2,060,805 discloses the dewax'ing of waxy distillates with a mixture of methyl ethyl ketone and toluone. As another group of solvent mixtures, the precipitating type component may be ethylene dichloride used in conjunction with a diluent type component which may be benzene, chloroform or carbon tetrachloride, or mixtures thereof. As another example, the precipitating component may be furfu-ral which may be used in conjunction with benzene as the diluent component. In the development of these prior art processes many modifications and improvements have ben made. In most instances, the ketone-aromatic solvent dewaxin-g process has been designed to produce lubricating oil fractions with natural pour points in the range of 0 F. to F.

It will be apparent to a workman skilled in the art that many other Well-known dewaxing solvents and solvent mixtures have the requisite characteristics for use as precipitant components and diluent components in the process of this invention. A workman skilled in the art may readily select a suitable precipitating solvent or solvent mixture for use with a diluent solvent or solvent mixture in the practice of the present invention.

In the lubricating oil field, at present, virtually all competitive lube oil base stocks are manufactured from Wax containing oils generally defined as parafiinic in nature. These parafinic oils are normally dewaxed to about 0 F. pour point for use in motor oils and industrial oils. The thus dewaxed oils are then treated with pour point depressants to obtain pour points in the range of from 30 to 50 F. The instant invention obviates the use of pour point depressants which are known to be both expensive and subject to degradation on prolonged use. The inexpensive lubricating oils resulting from the present process have low natural pour points and can be used for long periods of time in lubricating applications withice out attendant break-down and sludge formation which is somewhat characteristic of low pour point oils containing pour point depressants.

The present process encompasses the essential steps in the dewaxing of waxy crude oil distillates of (A) solvent dewaxin-g at a temperature of from -l0 to -20 F. and (B) again solvent dewaxing the oil from (A) at a temperature of from -60 to -90 F. to yield two types of usable wax and a low pour point lubricating oil as the products.

The present process provides low natural pour point oils from normally parafiinic hydrocarbons which has not heretofore been done by the standard ketone-aromatic or propane dewaxin g process. The present process provides two types of usable Wax and a low natural pour point oil which is useful as a motor oil, transformer oil, transmission fluid, refrigeration fluid, etc.

The process of this invention will be more fully illustrated by reference to the accompanying drawing wherein a specific embodiment of my invention is set forth. In the figure the waxy oil charge 1 is mixed with the methyl ethyl ketone-toluene solvent 2. The waxy oil-solvent mixture then passes to a double pipe exchanger 3 to exchange heat with the dewaxed oil mix stream from the filter 8. The charge mixture now passes to double pipe chiller 4 to chill the mixture to a filter .feed temperature of 10 to -20 F. Refrigeration for these chillers can come from ammonia or propane refrigation systems. The chilled charge mixture which now contains precipitated wax crystals passes to rotary drum filters 5 where wax is removed 11 and sent to a slack wax recovery system 12, the solvent 2 is recovered for re-use and the slack wax 15 is recovered for further process or used for catalytic cracking feed stock.

The dewaxed oil mixture at --10 to-ZO" F. now passes to another set of double pipe exchangers 6 to exchange heat with the returning dewaxed oil mixture stream 9 from rotary drum filters 8. The mixture then passes to double pipe chiller 7 to chill the mixture to -60 to 90 F. Refrigeration for these chillers can. come from an ethane or similar low temperature refrigeration system. This mixture now contains wax that has been precipitated out of solution. This mix passes to rotary drum filters 8 to remove the wax increment precipitated in this second pass of chilling. The dewaxed oil mixture at -60 to 90 F. 9 from the filters passes back through double pipe exchangers 6 and 3 to the dewaxed oil solvent recovery system 10. The solvent 2 is recovered and reused. The low temperature pour point dewaxed oils are recovered at 15. The present process may be combined with other refining processes such as a furfural or phenol extraction and acid treating, clay treating, caustic treating and hydrogenation. Clay treating, for instance, may be conducted using any natural or synthetic filtering medium and is conducted using treating conditions such as temperature, clay-to-oil ratios and either contact or percolation techniques designed to give the best results.

The soft waxes 13 from filters 8 pass to a solvent recovery system 14 where the solvent is recovered and reused 2. The soft waxes are recovered 17 and used as catalytic cracker feed stock or used to make chlorinated waxes.

The dewaxing solvents useful herein normally preferred are composed of from to 80% by volume of the ketone component and from 20 to 50% by volume of the aromatic component. In the present process it is proposed to use a blend of from to by volume of a ketone such as methyl ethyl ketone and from 30' to 40% by volume of an aromatic liquid such as toluene. The solvent to oil ratio will normally range from 1.01

to 6.021 by volume depending to a large extend upon the viscosity of the waxy oil charge.

The waxy crude oil distillates useful herein may be any paraffin base mineral oil typified by Mid-Continent Crude and Pennsylvania Crude oils.

The distillate preferably is solvent-extracted to remove aromatics prior to the dewaxing process. The solvent extraction step may be carried out using phenol or phenol containing 5-l5% water, or if so desired, any suitable phenol liquifying agent, such as glycerol, ethylene glycol and the like. Other materials such as liquid sulfur dioxide, furfural alcohols, nitrobenzene, beta, beta-dichloroethyl ether and dimethyl formamide, may also be used to remove aromatic, cyclic and resinous hydrocarbons from the raffinate phase.

When desired, the dewaxed lubricating oil stock is then treated with added hydrogen in the presence of a mild hydrogenation catalyst under conditions of temperature, pressure and feed stock space velocity to effect reactions whereby the characteristics of the oil being hydrogenated are altered to produce an oil product of im proved quality, i.e., increased stability to thin-film, high temperature oxidation.

Suitable mild hydrogenation catalysts that may be employed in the process of the invention are those formed from metals of the 6th and 8th group of the Periodic Table, their oxides or mixtures thereof.

Numerous hydrogenation catalysts have been proposed. Examples are nickel, molybdenum, tungsten vanadium, tin, zinc, chromium, iron and cobalt, and particularly the oxides and sulfides of these metals. Promoters comprising oxides of other metals have been used in admixture with such catalysts to increase their hydrogenating activ ity. Carriers such as alumina, silica gel, magnesium oxide and the like have also been employed. It is preferred to employ a molybdenum sulfide catalyst on an aluminum carrier, the catalyst containing essentially about 20% molybdenum sulfide on alumina.

Cobalt molybdate catalysts comprising mixtures of cobalt oxide have also been found to be satisfactory for use in the process of the invention. The cobalt molybdate catalyst known in the art generally contain from 5 to 45% of the combined oxides of cobalt and molybdenum in the molar ratio of from 0.5 to 5 mols of cobalt oxide per mol of molybdenum oxide. Such catalysts may also contain a stabilizer such as silica. Composite catalysts comprising alumina, platinum and combined halogen can also advantageously be used as the hydrogenation catalyst in the process of the invention. A nickel sulfide-tungsten sulfide hydrogenation catalyst is satisfactory. The operating temperature range for hydrogenation step can vary from about 400 F. to about 650 F. without adversely affecting the resultant product, but for maximum beneficial results, it is preferred to maintain the operating temperature at a range of from about 500 F. to 600 F. with a range of about 525 F. to 575 F. being especially preferred. Pressures varying from about 200' p.s.i.g. to about 2000 p.s.i.g. can be employed in the hydrogenation step with a pressure range that varies from about 500 p.s.i.g. to about 1000 p.s.i.g. being an especially preferred operating range.

Although the net consumption of hydrogen gas is somewhat dependent on the conditions of temperature, pressure and space velocity employed in the hydrogenation step, a representative value may vary from about 50 to 350 cubic feet of hydrogen per barrel of lubricating oil charged to the reactor.

The refrigerant used in the second dewaxing step of the present invention may be any of the known low tem perature refrigerants such as liquid ethane and some of the lower halogenated hydrocarbons such as the Freons.

The following examples are to be construed as illustrative only and not as limiting the scope of the invention.

Example I Table I shows the inspection data from the process 4 sequence in accordance with this invention wherein a waxy vacuum distillate charge was first extracted with furfural to yield a waxy raffinate (75% of the original waxy vacuum distillate) and finally the dewaxed, low pour point oil product.

The vacuum distillate was furfural extracted at a 20:1 by volume solventzoil ratio. The waxy raffinate thus obtained then was passed into the dewaxing unit more fully described herein and the waxy oil was mixed with a 65% methyl ethyl ketone-35% toluene mixture in a ratio of 1.5 :1 of solvent to oil. The mixture was then heated to 145 F. and then cooled by exchange with water, dewaxed oil and propane refrigeration at 20 F. Cold wash filtrate was added in the volume ratio of 1:1 for a total ratio of 2.5 :1 of solvent to oil to the filters. The wax cake was washed with cold solvent in a ratio of The dewaxed oil filtrate at -15 F. was passed to the second exchanger chiller train at a 30:1 solventzoil ratio to be chilled by dewaxed oil filtrate and Freon to -75 F. Some cold wash filtrate was recirculated to maintain a 5% solids concentration in the filter feed. The wax-oil slurry was filtered. A 1.5:1 solvent2oil ratio for washing the filter cake was used again at this point. The dewaxed oil, slack wax and soft waxes were then sent to their respective recovery systems. The dewaxed oil, slack wax and soft waxes were all commercially useful, per so without the necessity for further refinement or purification steps.

When another portion of the original waxy vacuum distillate charge described above was dewaxed in a single dewaxing step at -75 F., a much lower yield of oil having a pour point substantially higher than 50 F. was obtained and the single crude wax component was mixed with oil and was not commercially useful, per se.

Example 11 A transformer oil was prepared from a circulating gas oil stream which had the following inspection:

Gravity, API 32.4 Viscosity at F. SSU 5055 Flash, F 330 R1. at 140 F. 1.4655 Distillation at 760 mm.:

IBP F 550 EP F 750 Pour point, F +50 The above-described gas oil was extracted with furfural in a furfural extraction unit at 1.0:1 to 2.011 by volume solvent:oil ratio with a 100 F. bottom tower temperature and F. top tower temperature. The ramnate, which represented 7590% of the charge, Was then dewaxed by passing it to the dewaxing unit where the gas oil raflinate was mixed with a 65 by volume methyl ethyl ketone 35% by volume toluene solvent blend at a 3.0:1 to 4.0:1 by volume solventzoil ratio. This charge was passed through a double pipe exchanger and chiller train as described in Example I. The wax precipitated and the mixture was dewaxed on a rotary vacuum filter at 20 F. Approximately 18 to 25% of the charge precipitated as wax which was removed in this step. The dewaxed oil was then passed through the second exchanger chiller train and chilled to 65.

Gravity, API 33-34 Viscosity at 100 F 5863 Flash, F. 330 R.I. at 140 F. i 1.4500-1.4530 Distillation at 760 mm.:

IBP F 550 EP F 750 Pour point F 55 The dewaxed oil was then acid-treated with 95% sulfuric acid at 120 F. with a treat of 1 to 4 pounds of acid per barrel of oil. The oil was then caustic and water-washed. The oil was then decanted from the water and clay-treated with from 1 to 4 pounds of clay per barrel of oil at 300 F., filtered, sweetened and dried. The oil product without any added pour point depressant meets the standard transformer oil specifications.

Example III A low pour point, solvent refined lubricating oil stock suitable for motor oil blending and other automotive, aviation, or industrial oil applications was prepared from a vacuum unit distillate having the following typical inspections:

Gravity, API 31.5 Viscosity, SSU at 100 F 100-105 Viscosity, SSU at 210 F. 38-39 Pour point, F. +75 Color, O.D. 3.5 Distillation at 760 mm.:

IBP F 580 EP F 830 This distillate was furfural-extracted at a 2.021 by volume solvent2oil ratio with a 150 F. bottom tower temperature and 240 F. top tower temperature. The rafiinate thus obtained representing 75-85% of the charge was then dewaxed by the procedure of Example I. The waxy rafiinate was passed into the dewaxing unit where it was mixed with a 60% by volume methyl ethyl ketone-40% by volume toluene solvent blend at a 30:1 to 4.021 by volume solventzoil ratio. The charge mix was passed through a double pipe exchanger and chiller train as more fully described in Example I. The wax precipitated out and the mixture was dewaxed by filtration on a rotary vacuum filter at -20 F. Approximately 18 to 25% of the charge precipitated as wax which was removed in this step. The dewaxed oil mixture was then passed through the second exchanger chiller train and chilled to 65 F. The mixture was filtered the second time on a rotary vacuum filter to remove the second wax increment which represents of the charge. The dewaxed oil was then slurried with contacting clay at 380 F. with 0.5 to 4 pounds of clay per barrel of charge, the slurry was filtered and the oil was sweetened and dried. The finished oil had the following inspections:

Gravity, API 32.6 Viscosity at 100 F. 100105 This base stock was suitable for blending into finished automotive and other industrial oils.

I claim:

1. The process for preparing an oil having a natural pour point no higher than about 50' F. and usable wax from a wax bearing crude oil distillate comprising (A) forming a solution of a wax bearing crude oil distillate with a dewaxing solvent consisting of a mixture of an aliphatic ketone and an aromatic liquid and (B) precipitating wax from (A) by cooling to a temperature of from 0 to 20 F., recovering the precipitated wax and oil-solvent liquid therefrom and (C) further prepicitating wax from the oil-solvent liquid from (B) by cooling to a temperature of from to 90 F. and recovering the wax and low pour point oil therefrom.

2. The process of claim 1 wherein the wax-bearing crude oil distillate is first extracted with a solvent selected from the group consisting of furfural and a phenol.

3. The process of claim 2 wherein the mixture of an aliphatic ketone and an aromatic liquid is present in the r volume ratio of from 50:50 to :20 respectively.

4. The process of claim 3 wherein the volume ratio of dewaxing solvent to oil is from 1:1 to 6:1.

5. The process of claim 4 wherein the dewaxing solvent is a mixture of methyl ethyl ketone and toluene.

References Cited by the Examiner UNITED STATES PATENTS 2,054,433 9/1936 Manley 208-36 2,234,916 3/1941 Jones 208-33 2,246,982 6/1941 Nederbragt 208-33 2,265,139 12/1941 Brandt 208-33 2,397,868 4/1946 Jenkins 208-33 2,463,845 3/1949 Backlund et a1 208-33 2,754,250 7/1956 Shipman H 208-33 OTHER REFERENCES Petroleum Refiner, September 1960, vol. 39, No. 9, p. 243, or 1936, vol. 15, No. 6, p. 205.

DANIEL E. WYMAN, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner. H. LEVINE, P. KONOPKA, Assistant Examiner. 

1. THE PROCESS FOR PLREPARING AN OIL HAVING A NATURAL POUR POINT NO HIGHER THAN ABOUT -50*F. AND USABLE WAX FROM A WAX BEARING CRUDE OIL DISTILLATE COMPRISING (A) FORMING A SOLUTION OF A WAX BEARING CRUDE OIL DISTILLATE WITH A DEWAXING SOLVENT CONSISTING OF A MIXTURE OF AN ALIPHATIC KETONE AND AN AROMATIC LIQUID AND (B) PRECIPITATING WAX FROM (A) BY COOLING TO A TEMPERATURE OF FROM 0* TO -20*F., RECOVERING THE PRECIPITATED WAX AND OIL-SOLVENT LIQUID THEREFROM AND (C) FURTHER PREPICITATING WAX FROM THE OIL-SOLVENT LIQUID FROM (B) BY COOLING TO A TEMPERATURE OF FROM -60 TO -90*F. AND RECOVERING THE WAX AND LOW POUR POINT OIL THEREFROM. 